In order to increase the operational reliability of an optical transmission path, for example, with respect to the destruction of an optical waveguide connecting the two terminal nodes of the transmission path, it is known to provide a complete replacement path (protection path) for a working path, wherein, in the case of an interruption in the working path, the transmission is switched to the protection path. This case is called 1+1 protection.
For such 1+1 protection, the switching from the working path to the protection path is constructed such that the loss of the optical signal transmission via the working path is detected, and then the transmission is switched within a specified switchover time to the protection path. As the switchover time, for example, a maximum value of 50 ms is acceptable.
The detection of the functionality or the loss of the signal transmission via the working path is typically detected in the terminal nodes of the transmission path. Because the terminal nodes are typically located at the subscriber or at the customer of a network provider, it is necessary in such known transmission paths with 1+1 protection to install suitable active equipment at the site of the customer. In the case that a loss of the working path is detected, this equipment can generate a corresponding error signal and transmit this error signal to a network-management system that switches the transmission of the optical signal to the protection path. For this purpose, for example, in the terminal node, there can be a separate optical transmitter unit for signal transmission via a protection path connected to this node. Alternatively, the optical transmission signal may be fed by means of an optical switch, if necessary, to the working path or to the protection path.
A disadvantage in these known transmission paths with 1+1 protection, however, is the time and effort required with regard to the terminal node, i.e., at the site of the customer, for installing active equipment for switching the signal transmission from the working path to the protection path or vice versa. This is associated with an increase in the costs for the equipment technology at the site of the customer. In addition, this produces an increase in the costs for servicing the active equipment at the site of the customer.